1. Field of the Invention
The present invention relates to a pipe thickness measuring device and method, and recording medium and, in particular, to a technology of measuring a pipe thickness by using radiographic images of a pipe for the purpose of non-destructive inspection.
2. Description of the Related Art
Conventionally, as a device for measuring the thickness of a cylindrical body (hereinafter referred to as a “pipe”) by using radioactive rays, a device has been suggested, the device in which a sensor is located in a position where radioactive rays is emitted in parallel to a pipe tangential direction and where the radioactive rays having passed through the center of the pipe enters, and a pipe thickness is measured based on a amount of transmission radiation detected by the sensor (Japanese Patent Application Laid-Open No. 2009-36708).
Also, as a method of measuring a concrete thickness in a steel pipe configured by filling the inside of the steel pipe with concrete by centrifugal force, a method has been suggested in which: brightness information of each of radiographed images with different lengths of X-ray irradiation time is extracted; brightness distributions of the extraction results of the brightness information with a short irradiation time and the brightness information with a long irradiation time are combined; and an outer diameter of the steel pipe and an inner diameter of the concrete are estimated from an inflection point of the brightness distributions, thereby measuring a concrete thickness (Japanese Patent Application Laid-Open No. 2005-257610). Note that a known value or a value separately measured is used as the thickness of the steel pipe.
That is, in an image obtained by short-time X-ray irradiation, both edges of the steel pipe is clearly shown, but it is difficult to judge the state of the inside. On the other hand, in an image obtained by long-time X-ray irradiation, both edges of the steel pipe is blurred and unclear. To solve this problem, in the invention described in Japanese Patent Application Laid-Open No. 2005-257610,radiography with different lengths of X-ray irradiation time are performed to obtain images.
Also, it has been suggested that, in an X-ray CT device for constructing a tomogram of a subject to be shot along any slice surface, when a dimension between two edges specified on the tomogram is measured, position information of each edge is extracted from a differential value of line profile of CT values to a direction connecting the edges (Japanese Patent Application Laid-Open No. 2008-185359).